Focal cartilage defects are commonly found at arthroscopy for knee pain. These early signs of cartilage degeneration frequently do not affect the full thickness of the tissue and thus may be difficult to assess by surface imaging alone. Findings include blistering, fissuring, and fibrillation. Although debridement of focal cartilage defects is frequently performed in an attempt to slow progression of these defects, cross-sectional histological analysis shows that conventional arthroscopic surface imaging alone often yields incomplete debridement of abnormal cartilage or damage to adjacent normal cartilage. Our hypothesis is that intraoperative cross-sectional image guidance would allow the surgeon to more precisely identify, debride and stabilize damaged articular cartilage. Optical Coherence Tomography (OCT) is an echograph of infrared light that can provide the surgeon with cross-sectional images of articular cartilage at high resolution (10m) and in near real time allowing for potential intra-operative use. We have shown that OCT imaging of human articular cartilage has high agreement with histopathology, and we have successfully used OCT clinically during arthroscopic surgery to image articular cartilage. We now propose to perform studies to first determine whether cross-sectional imaging provides quantifiable information that can improve identification of early cartilage lesions. In the the first specific aim we will examine measures of the completeness of cartilage debridement and the volume of cartilage removed during debridement using cadveric knees with focal cartilage defects. Completeness of debridement will be assessed by the smoothness of the debrided residual cartilage, and by OCT and histomorphometry. Changes in cartilage volume will be assessed by 3.0T MRI. In the second aim, a randomized controlled clinical trial design will be utilized to examine the efficacy of OCT guided debridement in individuals with focal cartilage lesions in the medial and lateral femoral condyles. This aim will test the hypothesis that OCT-guided arthroscopic debridemeent of focal cartilage defects results in a smoother, and more stable articular surface as assessed by patient symptoms, function and 3.0 T MRI.